The present invention relates to a process for preparing N-alkylanilines and N-allylanilines. It relates more specifically to the preparation of N-allylanilines, and still more specifically to the preparation of N-monoallylanilines.
The preparation of N-monoallylanilines is especially important. For example, in the case of trifluoromethylaniline, the monoallyl derivative obtained is an important intermediate in the synthesis of a herbicide as described in French Patent 2,305,434. According to this patent, to prepare the desired herbicide, 1-[N-(meta-trifluoromethylphenyl)]-3-chloro-4-chloromethyl-2-pyrrolidone, it is necessary to start with a trifluoromethylaniline and protect one of the hydrogen atoms by adding an acetyl group before performing the allylation to create a monoallyltrifluoromethylaniline. The object of these extra steps is to avoid the formation of diallyl by-products which are unusable.
There has been a long-felt need in the industry to find a means of preparing a monoallyltrifluoromethylaniline directly in a single stage, instead of the three stages as described in French Patent 2,305,434, with good yields calculated with respect to the starting material employed, meta-trifluoromethylaniline, which is a very expensive compound which the industry has no wish to waste.
U.S. Pat. No. 4,701,560 attempted to solve this problem with a process for the allylation of meta-trifluoromethylaniline in a two-phase, water/organic solvent medium in the presence of an inorganic base chosen from carbonates or sodium hydroxide and in the presence of catalytic amounts of a quaternizable tertiary amine. To reduce the amount of undesirable diallyl by-products, it is necessary to limit the degree of conversion of the meta-trifluoromethylaniline, and hence to work in the presence of a deficiency of allyl halide; it is specified in this text that the ratio of meta-trifluoromethylaniline to the allyl halide is preferably approximately 2:1. Thus, the starting material is used in a non-stoichiometric amount and the yields of N-monoallyltrifluoromethylaniline calculated with respect to the meta-trifluoromethylaniline introduced do not exceed 40%. This is insufficient for an economically profitable and commercially successful process.
Allylation reactions with anilines other than meta-trifluoromethylaniline are also described. For example, U.S. Pat. No. 2,286,678 describes the allylation of para-hydroxyaniline in a medium consisting of an alcohol and in the presence of carbonate as a neutralizing agent.
The stated yields of N-monoallylhydroxyaniline do not exceed those of the previous patent. Also, this process results in the formation of a significant amount of diallyl derivatives which are undesirable biproducts. Therefore, this technique is also not applicable to the preparation of a N-monoallylated product in a single stage with good yield and little production of unwanted diallyl derivatives.
A process which consists of allylating 4-amino-diphenylamine with 2,3-dichloropropene in the presence of triethylamine is described in U.S. Pat. No. 3,668,254. The stated yields, as in the previous two processes, do not exceed 40%. In addition, triethylamine is used in a more than stoichiometric amount relative to the allyl halide. From an economic standpoint, this technique is disadvantageous on two accounts, the yields are low and the cost of the starting materials employed is too high.
U.S. Pat. No. 3,819,708 describes the alkylation of para-phenylenediamines in various solvents, in the presence of a tertiary amine such as triethylamine or an inorganic base as a neutralizing agent for the hydracid formed. The alkylating agents which are described are much less reactive than allyl halides, and the problem of dialkylation is hence much smaller. The selectivity, that is to say the yield of monoalkyl product relative to the dialkyl derivatives, is never described.
Despite the existence of an abundant literature describing the alkylation or allylation of various anilines, no process has ever been developed which solves the problems of preparing a N-monoalkylaniline or N-monoallylaniline that produces a good yield and very little unusable dialkyl or diallyl by-products. In other words, a process where there is a good degree of conversion of the starting aniline and good selectivity for the aniline monosubstituted on the nitrogen instead of the aniline disubstituted on the nitrogen.
It is an object of the present invention to provide a new process for producing N-alkylation and N-allylation of an aniline which avoids the disadvantages of previously-known processes. The new process will enable someone skilled in the art to produce high yields of N-monoalkylated or N-monoallylated anilines with very low formation of unusable dialkyl or diallyl derivatives.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of instrumentalities and combinations particularly pointed out in the appended claims.